The use of separate main contacts and arcing contacts within a circuit interrupting device is described within U.S. Pat. No. 4,039,983, in the names of Claude Terracol et al. and British Patent Specification No. 1,103,746, in the name of Narodni Podnik. In both the aforementioned U.S. Patent and British Patent Specification, current transfers through the main and arcing contacts until the main contacts become separated.
U.S. patent application Ser. No. 674,810, filed Nov. 26, 1984, in the name of E. K. Howell, entitled "Current Limiting Circuit Breaker", describes a high speed current limiting circuit interrupter utilizing a pair of main contacts electrically connected in parallel with a pair of arcing contacts arranged at the ends of movable contact arms. At the instant of separation of the main contacts, the circuit current transfers to the arcing contacts causing the arms to separate by electromagnetic repulsion creating an arc, which is subsequently extinguished within an arc chute.
The advantages of main and arcing contacts are described within the aforementioned U.S. patent application and include the use of a highly conductive metal for the main contacts to carry continuous current along with the use of a refractory metal for the arcing contacts. Further described within the aforementioned U.S. patent application is the expediency of arranging the arcing contacts at the ends of thin contact arms, which do not carry current on a continuing basis.
In the aforementioned current limiting circuit interrupter designs wherein the main contacts and the arcing contacts are electrically connected in parallel, relatively large currents may pass through the arcing contacts until such time as the contacts become electromagnetically repulsed and an arc ensues. The contacts and contact carrying arms must be heavy enough to sustain the large currents without becoming heated.
The instant invention provides a contact arrangement between the main and arcing contacts which assures that the arcing contacts do not become connected within the protected circuit until the main contacts have already started to separate.